Peacock needs to play the AFL to get his innings up. If he's called up he'll get, at most, 20 innings. He's thrown 140+ three seasons in a row. They need to get him to at least 160 this season if they want to use him as a starter.
On top of that, his change isn't there yet. He's doubled his walk rate from double A. If they intend to keep him as a starter, he needs to work on his change some more.